text: /*-------------------------------------------------------------------------
   *
   * tuptable.h
   *	  tuple table support stuff
   *
   *
   * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/executor/tuptable.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef TUPTABLE_H
  #define TUPTABLE_H
  
  #include "access/htup.h"
  #include "access/sysattr.h"
  #include "access/tupdesc.h"
  #include "access/htup_details.h"
  #include "storage/buf.h"
  
  /*----------
   * The executor stores tuples in a "tuple table" which is a List of
   * independent TupleTableSlots.
   *
   * There's various different types of tuple table slots, each being able to
   * store different types of tuples. Additional types of slots can be added
   * without modifying core code. The type of a slot is determined by the
   * TupleTableSlotOps* passed to the slot creation routine. The builtin types
   * of slots are
   *
   * 1. physical tuple in a disk buffer page (TTSOpsBufferHeapTuple)
   * 2. physical tuple constructed in palloc'ed memory (TTSOpsHeapTuple)
   * 3. "minimal" physical tuple constructed in palloc'ed memory
   *    (TTSOpsMinimalTuple)
   * 4. "virtual" tuple consisting of Datum/isnull arrays (TTSOpsVirtual)
   *
   *
   * The first two cases are similar in that they both deal with "materialized"
   * tuples, but resource management is different.  For a tuple in a disk page
   * we need to hold a pin on the buffer until the TupleTableSlot's reference
   * to the tuple is dropped; while for a palloc'd tuple we usually want the
   * tuple pfree'd when the TupleTableSlot's reference is dropped.
   *
   * A "minimal" tuple is handled similarly to a palloc'd regular tuple.
   * At present, minimal tuples never are stored in buffers, so there is no
   * parallel to case 1.  Note that a minimal tuple has no "system columns".
   * (Actually, it could have an OID, but we have no need to access the OID.)
   *
   * A "virtual" tuple is an optimization used to minimize physical data copying
   * in a nest of plan nodes.  Until materialized pass-by-reference Datums in
   * the slot point to storage that is not directly associated with the
   * TupleTableSlot; generally they will point to part of a tuple stored in a
   * lower plan node's output TupleTableSlot, or to a function result
   * constructed in a plan node's per-tuple econtext.  It is the responsibility
   * of the generating plan node to be sure these resources are not released for
   * as long as the virtual tuple needs to be valid or is materialized.  Note
   * also that a virtual tuple does not have any "system columns".
   *
   * The Datum/isnull arrays of a TupleTableSlot serve double duty.  For virtual
   * slots they are the authoritative data.  For the other builtin slots,
   * the arrays contain data extracted from the tuple.  (In this state, any
   * pass-by-reference Datums point into the physical tuple.)  The extracted
   * information is built "lazily", ie, only as needed.  This serves to avoid
   * repeated extraction of data from the physical tuple.
   *
   * A TupleTableSlot can also be "empty", indicated by flag TTS_FLAG_EMPTY set
   * in tts_flags, holding no valid data.  This is the only valid state for a
   * freshly-created slot that has not yet had a tuple descriptor assigned to
   * it.  In this state, TTS_SHOULDFREE should not be set in tts_flags, tts_tuple
   * must be NULL and tts_nvalid zero.
   *
   * The tupleDescriptor is simply referenced, not copied, by the TupleTableSlot
   * code.  The caller of ExecSetSlotDescriptor() is responsible for providing
   * a descriptor that will live as long as the slot does.  (Typically, both
   * slots and descriptors are in per-query memory and are freed by memory
   * context deallocation at query end; so it's not worth providing any extra
   * mechanism to do more.  However, the slot will increment the tupdesc
   * reference count if a reference-counted tupdesc is supplied.)
   *
   * When TTS_SHOULDFREE is set in tts_flags, the physical tuple is "owned" by
   * the slot and should be freed when the slot's reference to the tuple is
   * dropped.
   *
   * tts_values/tts_isnull are allocated either when the slot is created (when
   * the descriptor is provided), or when a descriptor is assigned to the slot;
   * they are of length equal to the descriptor's natts.
   *
   * The TTS_FLAG_SLOW flag is saved state for
   * slot_deform_heap_tuple, and should not be touched by any other code.
   *----------
   */
  
  /* true = slot is empty */
  #define			TTS_FLAG_EMPTY			(1 << 1)
  #define TTS_EMPTY(slot)	(((slot)->tts_flags & TTS_FLAG_EMPTY) != 0)
  
  /* should pfree tuple "owned" by the slot? */
  #define			TTS_FLAG_SHOULDFREE		(1 << 2)
  #define TTS_SHOULDFREE(slot) (((slot)->tts_flags & TTS_FLAG_SHOULDFREE) != 0)
  
  /* saved state for slot_deform_heap_tuple */
  #define			TTS_FLAG_SLOW		(1 << 3)
  #define TTS_SLOW(slot) (((slot)->tts_flags & TTS_FLAG_SLOW) != 0)
  
  /* fixed tuple descriptor */
  #define			TTS_FLAG_FIXED		(1 << 4)
  #define TTS_FIXED(slot) (((slot)->tts_flags & TTS_FLAG_FIXED) != 0)
  
  struct TupleTableSlotOps;
  typedef struct TupleTableSlotOps TupleTableSlotOps;
  
  /* base tuple table slot type */
  typedef struct TupleTableSlot
  {
  	NodeTag		type;
  #define FIELDNO_TUPLETABLESLOT_FLAGS 1
  	uint16		tts_flags;		/* Boolean states */
  #define FIELDNO_TUPLETABLESLOT_NVALID 2
  	AttrNumber	tts_nvalid;		/* # of valid values in tts_values */
  	const TupleTableSlotOps *const tts_ops; /* implementation of slot */
  #define FIELDNO_TUPLETABLESLOT_TUPLEDESCRIPTOR 4
  	TupleDesc	tts_tupleDescriptor;	/* slot's tuple descriptor */
  #define FIELDNO_TUPLETABLESLOT_VALUES 5
  	Datum	   *tts_values;		/* current per-attribute values */
  #define FIELDNO_TUPLETABLESLOT_ISNULL 6
  	bool	   *tts_isnull;		/* current per-attribute isnull flags */
  	MemoryContext tts_mcxt;		/* slot itself is in this context */
  	ItemPointerData tts_tid;	/* stored tuple's tid */
  	Oid			tts_tableOid;	/* table oid of tuple */
  } TupleTableSlot;
  
  /* routines for a TupleTableSlot implementation */
  struct TupleTableSlotOps
  {
  	/* Minimum size of the slot */
  	size_t		base_slot_size;
  
  	/* Initialization. */
  	void		(*init) (TupleTableSlot *slot);
  
  	/* Destruction. */
  	void		(*release) (TupleTableSlot *slot);
  
  	/*
  	 * Clear the contents of the slot. Only the contents are expected to be
  	 * cleared and not the tuple descriptor. Typically an implementation of
  	 * this callback should free the memory allocated for the tuple contained
  	 * in the slot.
  	 */
  	void		(*clear) (TupleTableSlot *slot);
  
  	/*
  	 * Fill up first natts entries of tts_values and tts_isnull arrays with
  	 * values from the tuple contained in the slot. The function may be called
  	 * with natts more than the number of attributes available in the tuple,
  	 * in which case it should set tts_nvalid to the number of returned
  	 * columns.
  	 */
  	void		(*getsomeattrs) (TupleTableSlot *slot, int natts);
  
  	/*
  	 * Returns value of the given system attribute as a datum and sets isnull
  	 * to false, if it's not NULL. Throws an error if the slot type does not
  	 * support system attributes.
  	 */
  	Datum		(*getsysattr) (TupleTableSlot *slot, int attnum, bool *isnull);
  
  	/*
  	 * Make the contents of the slot solely depend on the slot, and not on
  	 * underlying resources (like another memory context, buffers, etc).
  	 */
  	void		(*materialize) (TupleTableSlot *slot);
  
  	/*
  	 * Copy the contents of the source slot into the destination slot's own
  	 * context. Invoked using callback of the destination slot.
  	 */
  	void		(*copyslot) (TupleTableSlot *dstslot, TupleTableSlot *srcslot);
  
  	/*
  	 * Return a heap tuple "owned" by the slot. It is slot's responsibility to
  	 * free the memory consumed by the heap tuple. If the slot can not "own" a
  	 * heap tuple, it should not implement this callback and should set it as
  	 * NULL.
  	 */
  	HeapTuple	(*get_heap_tuple) (TupleTableSlot *slot);
  
  	/*
  	 * Return a minimal tuple "owned" by the slot. It is slot's responsibility
  	 * to free the memory consumed by the minimal tuple. If the slot can not
  	 * "own" a minimal tuple, it should not implement this callback and should
  	 * set it as NULL.
  	 */
  	MinimalTuple (*get_minimal_tuple) (TupleTableSlot *slot);
  
  	/*
  	 * Return a copy of heap tuple representing the contents of the slot. The
  	 * copy needs to be palloc'd in the current memory context. The slot
  	 * itself is expected to remain unaffected. It is *not* expected to have
  	 * meaningful "system columns" in the copy. The copy is not be "owned" by
  	 * the slot i.e. the caller has to take responsibility to free memory
  	 * consumed by the slot.
  	 */
  	HeapTuple	(*copy_heap_tuple) (TupleTableSlot *slot);
  
  	/*
  	 * Return a copy of minimal tuple representing the contents of the slot.
  	 * The copy needs to be palloc'd in the current memory context. The slot
  	 * itself is expected to remain unaffected. It is *not* expected to have
  	 * meaningful "system columns" in the copy. The copy is not be "owned" by
  	 * the slot i.e. the caller has to take responsibility to free memory
  	 * consumed by the slot.
  	 */
  	MinimalTuple (*copy_minimal_tuple) (TupleTableSlot *slot);
  };
  
  /*
   * Predefined TupleTableSlotOps for various types of TupleTableSlotOps. The
   * same are used to identify the type of a given slot.
   */
  extern PGDLLIMPORT const TupleTableSlotOps TTSOpsVirtual;
  extern PGDLLIMPORT const TupleTableSlotOps TTSOpsHeapTuple;
  extern PGDLLIMPORT const TupleTableSlotOps TTSOpsMinimalTuple;
  extern PGDLLIMPORT const TupleTableSlotOps TTSOpsBufferHeapTuple;
  
  #define TTS_IS_VIRTUAL(slot) ((slot)->tts_ops == &TTSOpsVirtual)
  #define TTS_IS_HEAPTUPLE(slot) ((slot)->tts_ops == &TTSOpsHeapTuple)
  #define TTS_IS_MINIMALTUPLE(slot) ((slot)->tts_ops == &TTSOpsMinimalTuple)
  #define TTS_IS_BUFFERTUPLE(slot) ((slot)->tts_ops == &TTSOpsBufferHeapTuple)
  
  
  /*
   * Tuple table slot implementations.
   */
  
  typedef struct VirtualTupleTableSlot
  {
  	TupleTableSlot base;
  
  	char	   *data;			/* data for materialized slots */
  } VirtualTupleTableSlot;
  
  typedef struct HeapTupleTableSlot
  {
  	TupleTableSlot base;
  
  #define FIELDNO_HEAPTUPLETABLESLOT_TUPLE 1
  	HeapTuple	tuple;			/* physical tuple */
  #define FIELDNO_HEAPTUPLETABLESLOT_OFF 2
  	uint32		off;			/* saved state for slot_deform_heap_tuple */
  	HeapTupleData tupdata;		/* optional workspace for storing tuple */
  } HeapTupleTableSlot;
  
  /* heap tuple residing in a buffer */
  typedef struct BufferHeapTupleTableSlot
  {
  	HeapTupleTableSlot base;
  
  	/*
  	 * If buffer is not InvalidBuffer, then the slot is holding a pin on the
  	 * indicated buffer page; drop the pin when we release the slot's
  	 * reference to that buffer.  (TTS_FLAG_SHOULDFREE should not be set in
  	 * such a case, since presumably tts_tuple is pointing into the buffer.)
  	 */
  	Buffer		buffer;			/* tuple's buffer, or InvalidBuffer */
  } BufferHeapTupleTableSlot;
  
  typedef struct MinimalTupleTableSlot
  {
  	TupleTableSlot base;
  
  	/*
  	 * In a minimal slot tuple points at minhdr and the fields of that struct
  	 * are set correctly for access to the minimal tuple; in particular,
  	 * minhdr.t_data points MINIMAL_TUPLE_OFFSET bytes before mintuple.  This
  	 * allows column extraction to treat the case identically to regular
  	 * physical tuples.
  	 */
  #define FIELDNO_MINIMALTUPLETABLESLOT_TUPLE 1
  	HeapTuple	tuple;			/* tuple wrapper */
  	MinimalTuple mintuple;		/* minimal tuple, or NULL if none */
  	HeapTupleData minhdr;		/* workspace for minimal-tuple-only case */
  #define FIELDNO_MINIMALTUPLETABLESLOT_OFF 4
  	uint32		off;			/* saved state for slot_deform_heap_tuple */
  } MinimalTupleTableSlot;
  
  /*
   * TupIsNull -- is a TupleTableSlot empty?
   */
  #define TupIsNull(slot) \
  	((slot) == NULL || TTS_EMPTY(slot))
  
  /* in executor/execTuples.c */
  extern TupleTableSlot *MakeTupleTableSlot(TupleDesc tupleDesc,
  										  const TupleTableSlotOps *tts_ops);
  extern TupleTableSlot *ExecAllocTableSlot(List **tupleTable, TupleDesc desc,
  										  const TupleTableSlotOps *tts_ops);
  extern void ExecResetTupleTable(List *tupleTable, bool shouldFree);
  extern TupleTableSlot *MakeSingleTupleTableSlot(TupleDesc tupdesc,
  												const TupleTableSlotOps *tts_ops);
  extern void ExecDropSingleTupleTableSlot(TupleTableSlot *slot);
  extern void ExecSetSlotDescriptor(TupleTableSlot *slot, TupleDesc tupdesc);
  extern TupleTableSlot *ExecStoreHeapTuple(HeapTuple tuple,
  										  TupleTableSlot *slot,
  										  bool shouldFree);
  extern void ExecForceStoreHeapTuple(HeapTuple tuple,
  									TupleTableSlot *slot,
  									bool shouldFree);
  extern TupleTableSlot *ExecStoreBufferHeapTuple(HeapTuple tuple,
  												TupleTableSlot *slot,
  												Buffer buffer);
  extern TupleTableSlot *ExecStorePinnedBufferHeapTuple(HeapTuple tuple,
  													  TupleTableSlot *slot,
  													  Buffer buffer);
  extern TupleTableSlot *ExecStoreMinimalTuple(MinimalTuple mtup,
  											 TupleTableSlot *slot,
  											 bool shouldFree);
  extern void ExecForceStoreMinimalTuple(MinimalTuple mtup, TupleTableSlot *slot,
  									   bool shouldFree);
  extern TupleTableSlot *ExecStoreVirtualTuple(TupleTableSlot *slot);
  extern TupleTableSlot *ExecStoreAllNullTuple(TupleTableSlot *slot);
  extern void ExecStoreHeapTupleDatum(Datum data, TupleTableSlot *slot);
  extern HeapTuple ExecFetchSlotHeapTuple(TupleTableSlot *slot, bool materialize, bool *shouldFree);
  extern MinimalTuple ExecFetchSlotMinimalTuple(TupleTableSlot *slot,
  											  bool *shouldFree);
  extern Datum ExecFetchSlotHeapTupleDatum(TupleTableSlot *slot);
  extern void slot_getmissingattrs(TupleTableSlot *slot, int startAttNum,
  								 int lastAttNum);
  extern void slot_getsomeattrs_int(TupleTableSlot *slot, int attnum);
  
  
  #ifndef FRONTEND
  
  /*
   * This function forces the entries of the slot's Datum/isnull arrays to be
   * valid at least up through the attnum'th entry.
   */
  static inline void
  slot_getsomeattrs(TupleTableSlot *slot, int attnum)
  {
  	if (slot->tts_nvalid < attnum)
  		slot_getsomeattrs_int(slot, attnum);
  }
  
  /*
   * slot_getallattrs
   *		This function forces all the entries of the slot's Datum/isnull
   *		arrays to be valid.  The caller may then extract data directly
   *		from those arrays instead of using slot_getattr.
   */
  static inline void
  slot_getallattrs(TupleTableSlot *slot)
  {
  	slot_getsomeattrs(slot, slot->tts_tupleDescriptor->natts);
  }
  
  
  /*
   * slot_attisnull
   *
   * Detect whether an attribute of the slot is null, without actually fetching
   * it.
   */
  static inline bool
  slot_attisnull(TupleTableSlot *slot, int attnum)
  {
  	AssertArg(attnum > 0);
  
  	if (attnum > slot->tts_nvalid)
  		slot_getsomeattrs(slot, attnum);
  
  	return slot->tts_isnull[attnum - 1];
  }
  
  /*
   * slot_getattr - fetch one attribute of the slot's contents.
   */
  static inline Datum
  slot_getattr(TupleTableSlot *slot, int attnum,
  			 bool *isnull)
  {
  	AssertArg(attnum > 0);
  
  	if (attnum > slot->tts_nvalid)
  		slot_getsomeattrs(slot, attnum);
  
  	*isnull = slot->tts_isnull[attnum - 1];
  
  	return slot->tts_values[attnum - 1];
  }
  
  /*
   * slot_getsysattr - fetch a system attribute of the slot's current tuple.
   *
   *  If the slot type does not contain system attributes, this will throw an
   *  error.  Hence before calling this function, callers should make sure that
   *  the slot type is the one that supports system attributes.
   */
  static inline Datum
  slot_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
  {
  	AssertArg(attnum < 0);		/* caller error */
  
  	if (attnum == TableOidAttributeNumber)
  	{
  		*isnull = false;
  		return ObjectIdGetDatum(slot->tts_tableOid);
  	}
  	else if (attnum == SelfItemPointerAttributeNumber)
  	{
  		*isnull = false;
  		return PointerGetDatum(&slot->tts_tid);
  	}
  
  	/* Fetch the system attribute from the underlying tuple. */
  	return slot->tts_ops->getsysattr(slot, attnum, isnull);
  }
  
  /*
   * ExecClearTuple - clear the slot's contents
   */
  static inline TupleTableSlot *
  ExecClearTuple(TupleTableSlot *slot)
  {
  	slot->tts_ops->clear(slot);
  
  	return slot;
  }
  
  /* ExecMaterializeSlot - force a slot into the "materialized" state.
   *
   * This causes the slot's tuple to be a local copy not dependent on any
   * external storage (i.e. pointing into a Buffer, or having allocations in
   * another memory context).
   *
   * A typical use for this operation is to prepare a computed tuple for being
   * stored on disk.  The original data may or may not be virtual, but in any
   * case we need a private copy for heap_insert to scribble on.
   */
  static inline void
  ExecMaterializeSlot(TupleTableSlot *slot)
  {
  	slot->tts_ops->materialize(slot);
  }
  
  /*
   * ExecCopySlotHeapTuple - return HeapTuple allocated in caller's context
   */
  static inline HeapTuple
  ExecCopySlotHeapTuple(TupleTableSlot *slot)
  {
  	Assert(!TTS_EMPTY(slot));
  
  	return slot->tts_ops->copy_heap_tuple(slot);
  }
  
  /*
   * ExecCopySlotMinimalTuple - return MinimalTuple allocated in caller's context
   */
  static inline MinimalTuple
  ExecCopySlotMinimalTuple(TupleTableSlot *slot)
  {
  	return slot->tts_ops->copy_minimal_tuple(slot);
  }
  
  /*
   * ExecCopySlot - copy one slot's contents into another.
   *
   * If a source's system attributes are supposed to be accessed in the target
   * slot, the target slot and source slot types need to match.
   */
  static inline TupleTableSlot *
  ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
  {
  	Assert(!TTS_EMPTY(srcslot));
  	AssertArg(srcslot != dstslot);
  
  	dstslot->tts_ops->copyslot(dstslot, srcslot);
  
  	return dstslot;
  }
  
  #endif							/* FRONTEND */
  
  #endif							/* TUPTABLE_H */
  